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Date: Mon, 31 Aug 2009 21:13:08 +0200
From: Milan Broz <mbroz@redhat.com>
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Subject: Re: [dm-crypt] [Request] cryptsetup option to fix leftovers from
 old	filesystems
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To: =?ISO-8859-15?Q?Thomas_B=E4chler?= <thomas@archlinux.org>
Cc: dm-crypt@saout.de, util-linux-ng@vger.kernel.org

Thomas B=E4chler wrote:
> We have encountered a problem with blkid that is caused by cryptsetup=20
> not cleaning superblocks of old filesystems on luksFormat. The problem=20
> has been fixed in 1.0.7, however old LUKS volumes still suffer from this =

> problem. Please read this thread for details:
>=20
> http://thread.gmane.org/gmane.linux.utilities.util-linux-ng/2563
>=20
> What I would request is an option to "clean" the unused area in the LUKS =

> header up to the start of the payload, such that for example an old ext2 =

> magic is removed. All that without destroying the used areas in the LUKS =

> header, of course.
>=20
> I'm not very familiar with the LUKS code or on-disk format, so I would=20
> be greatful if anyone who is would implement such a feature. Thanks for=20
> your replies.

Hi Thomas,

I don't think we need implement any clean function, new version already
wipes that area.

Because visible LUKS header is written in first 2 sectors and keyslot
area always begins on 4k offset, you can use this command to wipe unused ar=
ea
with possible old signature (at least this works for swap/luks signature mi=
smatch):

dd if=3D/dev/zero of=3D<device> bs=3D512 seek=3D2 count=3D6

But please create backup before trying this... ;-)

(btw mkswap should clean LUKS signature too - try mkswap over old LUKS
and then blkid:-)

Milan
--
mbroz@redhat.com